Method of forming metal blanks for sputtering targets

ABSTRACT

The present invention relates to an improvement in the manufacture of metal blanks, discs, and sputtering targets by flattening only one of the two surfaces of a metal plate. The elimination of flattening the metal plate&#39;s second surface results in a significant cost reduction. The metal plate of the present invention preferably has a single-side flatness of 0.005 inches or less, which improves the reliability of the bond between the target blank and a backing plate. Preferred metals include, but are not limited to, tantalum, niobium, titanium, and alloys thereof. The present invention also relates to machining the first side of a metal plate, bonding the first side to a backing plate, and then optionally machining the second side of the metal plate.

BACKGROUND OF THE INVENTION

The present invention relates to a method for making sputtering targetsthat reduces machine costs and improves quality and reliability,relative to conventional methods for preparing sputtering targets. Thepresent invention further relates to methods of preparing improved metaldiscs. The present invention also relates to a method for reducing themanufacturing costs of sputtering targets and/or metal discs.

In the field of metal fabrication in general, and sputtering targets inparticular, significant difficulties arise with regard to the costsassociated with producing planar discs with very highly specificdimensional requirements. It is common practice in the field ofmanufacturing a metal disc to flatten both sides of a metal blank whichis eventually formed into a metal disc, for example, a tantalumsputtering target preform. This requires the grinding of both sides ofthe metal blank, rolling both sides, or press flattening and/or surfaceconditioning of both sides of the metal.

Thus, for instance, a planar sputtering target preform can be machinedfrom a rolled metal plate. Other methods of manufacturing sputteringtarget preforms, such as forging and subsequently processing ofcylindrical metal billets, can be used. Typically, the dimensions of thesputtering target preform are larger than the dimensions of theresultant finished sputtering target blank after bonding onto a backingplate and finish machining operations are completed to produce asputtering target assembly.

The manufacturing of a planar tantalum sputtering target involves therolling of tantalum plate to a gauge that is typically 0.010-0.100inches greater than the thickness of the finish machined target blankand a thickness tolerance of about 5-10% of the rolled gauge, levelrolling to a nominal flatness of 0.050 inches, annealing the plate,rough cutting of blanks from the plate, several labor-intensiveiterations of manual press flattening and surface conditioning to attaina flatness of 0.010 inches or less, and then machining the blanks to adesired diameter. These preform blanks are then sold to a sputteringtarget manufacturer, who bonds the blank to a backing plate, and thenmachines the face and diameter of the bonded preform to the dimensionalrequirements for the assembled sputtering target as specified by thesputtering equipment Original Equipment Manufacturer (OEM) or the targetsupplier's customers.

However, often the final metal disc or sputtering target produced isutilized in an application where, in fact, only one side of the disc orsputtering target truly benefits from and/or needs the highly specificdimensional properties.

Because of the high intrinsic cost and value of, for instance, tantalum,efforts are commonly taken to reduce the generation of scrap in thevarious manufacturing processes associated with tantalum. The targetsuppliers place tight dimensional tolerances on gauge and diameters ofthe blanks to minimize the weight of the material they purchase.Furthermore, the target suppliers would prefer blanks that meet aflatness of 0.005 inches, which would significantly improve thereliability of the bond between the target blank and the backing plate.However, achieving such stringent tolerances in gauge and flatnessrequires the grinding and the lapping of the blanks, a process which isprohibitively expensive and generates excessive amounts of low-valuegrinding scrap called swarf. Typically, the value of the tantalumcontained in the swarf is less than the value of tantalum turningsgenerated by machining operations since it is often difficult andexpensive to separate the tantalum particles from the grinding mediacomprising the swarf, and because of the greater propensity forcontamination of the tantalum by grinding compared to machining.

Accordingly, there is a need to overcome one or more of the abovedescribed disadvantages.

SUMMARY OF THE INVENTION

A feature of the present invention is to provide a method to manufacturecost-effective metal products. The present invention relates to avoidingthe costs associated with time, labor, and lost metal material, whichincurs during the grinding of both surfaces of a metal planar object.

Another feature of the present invention is to modify the tolerances ofthe tantalum or other metal target blanks to thereby enhance productionof the metal blank, disc, and the sputtering target.

Another feature of the present invention is to provide a method formanufacturing metal blanks, by flattening only the first surface of aplate to a flatness of about 0.005 inch or less.

A further feature of the present invention is to provide a method formanufacturing metal discs.

Another further feature of the present invention is to provide a metalblank, which has been single-side machined, that can be bonded to abacking plate and the resulting composite subsequently shaped, cut, orconfigured to form a desired sputtering target.

A further feature of the present invention is to provide a method toimprove or reduce the cost of manufacturing metal blanks, discs, andmetal sputtering targets.

Another further feature of the present invention is to provide a methodfor manufacturing a metal article from a metal plate or a metal blankwhereby the value of the material removed from the article duringmanufacturing is maximized.

Another further feature of the present invention is to provide a methodfor manufacturing a metal article that reduces the amount ofcontamination of the removed material.

Another feature of the present invention is to provide a method forreducing the cost of manufacturing a metal disc from a metal plate or ametal blank.

A further feature of the present invention is to provide a method forreducing the cost of manufacturing a metal sputtering target from aplate, a blank, or a disc.

Additional features and advantages of the present invention will be setforth in part in the description that follows, and in part will beapparent from the description, or may be learned by practice of thepresent invention. The objectives and other advantages of the presentinvention will be realized and attained by means of the elements andcombinations particularly pointed out in the written description andappended claims.

To achieve these objectives and other advantages and in accordance withthe purposes of the present invention, as embodied and broadly describedherein, the present invention relates to a method of manufacturing ametal blank or a disc by supplying at least one planar metal platehaving a first surface and a second surface, wherein the first and thesecond surfaces are essentially parallel; and flattening only the firstsurface of the plate to about 0.005 inches or less, whereby a metalblank is produced.

The present invention also relates to a method of forming a sputtertarget assembly by providing a metal sputter target preform whichcomprises a metal disc, providing a backing plate and providing anoptional bonding agent, and subjecting the target preform, backing plateand optional bonding agent to a sufficient temperature and a sufficientpressure for a sufficient time to provide, accept, or achieve a bondbetween the metal target and the backing plate

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide a further explanation of the presentinvention as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional schematic diagram of a rolled metal plateand a sputter target that is produced after machining said rolled metalplate.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention relates to supplying metal blanks, discs, andsputtering targets with one flat side. Having only one flat surface orside can offer several benefits as compared to the conventional metaldisc production process.

For the purposes of the present invention “essentially parallel” can bedefined as planes which do not intersect. Thus, it is not a criticallimitation of the present invention for the surfaces of the metal plateto exhibit highly specific dimensional properties, such as absoluteparallel surfaces. A person skilled in the art can determine the degreeof deviation of the surfaces of the metal plate, blank, disc, and/orsputtering target from true parallel, which can be effective within thepresent invention.

In general, “blanks” can be defined as metal bodies useful for thefabrication of discs and/or sputtering targets. No specific limitationson dimensions of the blanks are known within the present invention. Ingeneral, the terms “blanks” and “preforms” can be used interchangeably.In general, “metal plate” can be defined as any metal in continuousform, such as extruded, pressed or rolled ingot-metallurgy orpowder-metallurgy derived sheet or billet or other non-powder ornon-flaked form.

In general, “a flatness of X inches” can be understood as the measure ofdeviation from flat, or a perfect plane, at any one point relative tothe total surface, where flat is 0.000 inches.

In general, “disc” can be understood as, inter alia, a right circularcylinder with a thickness to diameter ratio of 1 or less. “Disc” hereinalso includes ovals, triangles, rectangles, and other polygons. When adisc is a rectangle, it preferably includes corners that are at leastpartially rounded. There are no known size limitations on the disc ofthe present invention.

In general, “sputtering target” can be understood as a source materialfor depositing thin films such as by physical vapor deposition. Commonsputtering target materials useful herein include, but are not limitedto, metal, such as tantalum, copper, titanium, cobalt, niobium,platinum, silver, gold, aluminum, and combinations thereof or alloysthereof.

In general, “backing plate” can be understood as any material, chemicalcompound, metallic substrate, adhesive, foundation or other structuralsupport which can contact the blank, disc, or sputtering target. Themetals above are also examples of suitable metals for the backing plate.

In general, “bonding agent” can be defined as any material, chemicalcompound, metallic substrate, adhesive, foundation or other structuralsupport which promotes the formation of a bond between the blank and thebacking plate.

In general, grinding is defined as the process of removing material fromwork-pieces by the cutting action of a solid, rotating, grinding wheelcomposed of abrasive grains or grit plus a bonding material.

In general, machining is defined as any process to remove material froma metal plate or disc by using a non-consumable tool bit without usingabrasive grains or grit that can be dislodged to contaminate the scrapmetal.

In the present invention, the words “face”, “side,” and “surface” may beused interchangeably.

In the present invention, the words “sputtering target” and “sputtertarget” may be used interchangeably.

Flattening one surface of a metal can remove any surface imperfections,such as ripples, voids, concavities, or convexities that can hinder thebonding integrity.

Having only one flat surface can minimize or completely eliminateiterative press flattening operation, since the primary purpose of thepress flattening operation is to produce preforms having faces that aresufficiently flat to allow for subsequent bonding to the backing plates.Press flattening has been identified as the cost driver in the machiningcost of manufacturing metal target blanks, which represents thebottleneck in the blank machining process. While this process maynecessitate increasing the gauge tolerance of the blank to assure thatthe blanks meet the finished tolerances after the bonding and machiningsteps, the expectant savings in labor and inventory costs will more thanoffset the slight additional material yield costs. Any additionalmanufacturing costs incurred by the target suppliers will be minimal,since no new machining steps are being introduced or required by thepresent invention.

Further, in addition to the actual loss of metal in unnecessary grindingsteps, the value of the scrap itself can be significantly improved orincreased by the present invention. Swarf value recovered from thegrinding of both surfaces of a tantalum disc has a current value ofabout fifty dollars ($50.00) per pound of contained tantalum because thegrinding materials dislodged from the grinder can mix with the scrapmetal as impurities and lower the value of the scrap metal. Tantalum canbe recovered from grinding swarf using the same chemical separation andreduction processes employed to refine tantalum from raw ore. Also,mechanical separation processes, such as but not limited to, gravityseparation, frothing, or magnetic separation can also be used, but theseprocesses are inefficient in separating all of the tantalum and thegrinding media leading to low tantalum reclaim yields, and isinefficient in separating all of the grinding media from the tantalum,resulting in contamination of the tantalum. As such, the value of thetantalum in grinding swarf is similar to the value of tantalum in nativeore. The scrap metal recovered from machining of a single surface of atantalum disc has a current value of approximately one hundred dollars($100.00) per pound of contained metal because machining does notintroduce any contaminants or only introduces negligible amount ofcontaminants into the scrap metal. Tantalum machining scrap can bereadily melted into tantalum ingots without the need for chemicalrefining and reduction processes, and hence retains the value-added fromthese processes.

Thus, producing metal target blanks with one flat surface results insignificant savings in manufacturing costs, and a subsequent increase inmachine shop throughput. The present invention is therefore ideal formaterials with a large spread in scrap grade value, e.g., tantalum, highpurity copper, and titanium, and the like.

In a similar manner, significant cost savings can result during thesubsequent preparation of the disc and sputtering targets.

Preferably, the metal blank, disc, and sputtering target having only oneflat side are made from valve metals or other metals. Preferably, theyare made from, for example, tantalum, copper, aluminum, titanium,niobium, cobalt, platinum, silver, and gold. Other examples includealloys containing one or more of these metals. A preferred metal istantalum.

Preferably, the flat surface of the metal blank, disc, or sputteringtarget has a flatness of from about 0.060 inches to about 0.001 inches,and more preferably, has a flatness of about 0.005 inches or less.Preferably, the metal blank has a nominal thickness tolerance of+0.100/−0.00 inches for blank thicknesses of from about 0.250 to about0.500 inches, and +0.050/−0.00 inches for blank thicknesses less thanabout 0.250 inches. The nominal diameter tolerances according to thepresent invention can be +0.025/−0.00 inches for discs having diametersof from about 2 to about 24 inches. Preferably, the metal blank has anominal thickness tolerance of at least about 5% of the rolled gauge ofthe plate and more preferably, a tolerance of from about 5% to about 10%of the rolled gauge of the plate. The non-flattened surface, or thesecond surface, of the metal blank, disc, or sputtering target can havea flatness of from about 0.010 inches or less to about 0.075 inches ormore. Preferably, the second surface has a flatness of from about 0.025inches or less, and more preferably, the second surface has a flatnessof from about 0.015 inches or less.

In one example, a metal blank with a first surface machined or otherwiseconditioned to a flatness of 0.005 inches or less can first be shapedinto a disc and then be fixed to a backing plate, or can immediately bebonded to a backing plate and later be altered or redefined.

In one example, the second surface of the metal blank is also flattened.Supplying metal blanks, discs, and sputtering targets with both sidesflattened by machining can offer several benefits compared to theconventional metal discs produced by grinding.

The second surface or side of the metal blank, disc, or sputteringtarget can be machined to a flatness of from about 0.025 inches or lessand preferably the second side is machined to a flatness of about 0.005inches or less. The machining of the second surface can be donefollowing the bonding of the sputtering target preform onto the backingplate as part of the finish machining step of the assembled sputteringtarget.

As stated earlier, machining a metal plate does not introduce or onlyintroduces a negligible amount of contaminants to the scrap metal. Thus,the scrap metal produced by machining both sides of a metal plate has ahigher value (current value of about $100 per pound) than the scrapmetal produced by grinding both sides of a metal plate (current value ofabout $50 per pound contained tantalum). Thus, machining both surfacesof a metal plate instead of grinding reduces the overall cost ofproducing metal blanks, discs, and sputtering targets.

The method for producing a sputtering target assembly is not limited tothe order or sequence of the steps in the fabrication of a sputteringtarget. The method for forming a sputtering target assembly preferablyincludes connecting or affixing a sputter target, such as a metal blankor a metal disc to a backing plate.

Any method known to one skilled in the art can be used to connect oraffix the sputter target to a backing plate. For example, the sputtertarget can be adjoined to the backing plate or backing plate precursorcomposition by using an adhesive material, by pressure-fitting, by hotmelting, by soldering, by brazing, by diffusion bonding, explosionbonding, or by using a mechanical device, such as a clamp.

Furthermore, the sputter target assembly can optionally contain aninterlayer material that can act as a bonding aid between the targetblank and the backing plate. The interlayer material can be in the formof a thin film coating applied by electroplating, electroless plating,vapor deposition, ion beam deposition, or other suitable means fordepositing a thin film. The interlayer can also be in the form of afoil, plate, or block. Examples of interlayer materials can include, butare not limited to, zirconium as found in U.S. Pat. No. 6,376,281,titanium as found in U.S. Pat. No. 5,863,398 and U.S. Pat. No.6,071,389, copper, aluminum, silver, nickel, and alloys thereof, asfound in U.S. Pat. No. 5,693,203, and graphite as found in U.S. Pat. No.6,183,613 B1, each of which is incorporated in its entirety by referenceherein.

The backing plate, interlayer and/or bonding agent can be made from anymaterial, chemical compound, metallic substrate, adhesive, or foundationthat can provide structural support.

In one example, the second surface is flattened after the first surfacehas achieved a flatness of about 0.005 inches or less. Preferably, thesecond surface is flattened after the metal blank is adjoined to abacking plate. Preferably, the second surface of the target is flattenedby machining. The backing plate can provide ample support when machiningthe second surface of the target. By not providing a backing plate tosupport the target, the target can bend. Thus, there would be a need toonly partially machine the first surface, then partially machine thesecond surface, and continue altering between the first surface and thesecond surface to prevent bends from forming in the target. This processwould be very time-consuming and expensive. Also, machining of thesecond surface after bonding to the backing plate is typically necessaryto assure the dimensional specifications defined by the OEM or targetmanufacturer. Therefore, the use of a backing plate when machining thesecond surface can reduce the cost of production and avoid redundantmachining operations.

A preferred method to manufacture the metal blanks, which can be part ofthe sputtering target of the present invention, includes supplying atleast one metal plate having a first surface and a second surface,wherein the first and the second surfaces are essentially parallel.Preferably, the first surface of the metal plate is flattened to form ametal blank, which can then either be shaped to a disc, which is thenaffixed to a backing plate, or the flattened first surface of the metalblank can be directly affixed (e.g., bonded) to the backing plate, whoseshape can later be altered or re-defined.

The sequence of steps recited in the present invention is not criticalto the invention. Thus, for example, one skilled in the art can roll outthe metal plate into a sheet, which has been single-face machined toform a blank, then cut, machine, or otherwise shape the blank to form adisc. The disc can then be affixed to a backing plate to form asputtering target assembly. Alternatively, one can cut the shape andsize of the desired final sputtering target, or the disc and thenmachine the first surface to its desired flatness.

Preferably, the first surface of a metal is flattened from about 0.025inches or less and more preferably it is flattened to about 0.005 inchesor less. Preferably, the first surface of the metal blank is flattenedby a machining process. As stated earlier, the scrap metal from amachining process has a higher value than the scrap metals from agrinding process because machining does not introduce any contaminantsor only introduces a negligible amount of contaminants into the scrapmetal. Thus, the grinding swarf can have a value of about $50 per poundof contained tantalum, while the scrap metal recovered from machiningcan have a value of about $100 per pound.

Preferably, the machining process, which flattens the first surface toabout 0.005 inches or less provides a nominal thickness tolerance of+0.100/−0.00 inches for a blank thickness of from about 0.250 to about0.500 inches and a nominal thickness tolerance of +0.050/−0.00 for blankthickness of about 0.250 inches or less.

The second surface of the metal blank, which is preferably not machinedat this time, can have a flatness of from about 0.075 inches or less andpreferably 0.025 inches or less. Preferably, the process for forming ametal sheet creates a second surface which includes a flatness of fromabout 0.060 inches to about 0.005 inches, and more preferably, of fromabout 0.030 inches to about 0.005 inches. The second surface can beflattened by level rolling of the plate, stretching flattening, pressflattening, milling, grinding, or lapping of the metal plate or thesputtering target blank.

In another example, one can start with a cylinder or billet of metal,such as tantalum, which is then forged to form a round-shaped planarobject, which can be machined into a disc. For purposes of thisinvention, a blank and/or a plate can include billets (e.g. forgedbillets) and the like.

The present invention will be further clarified by the followingexamples, which are intended to exemplary of the present invention.

EXAMPLES Example 1

FIG. 1 shows a rolled metal plate (10) having an as-rolled oras-level-rolled flatness designated “f” and an initialized gaugethickness of “g.” A planar sputtering target (20) of finished thickness“t” can be produced. Generally, the relationship between initialthickness with respect to initial flatness and finished thickness isg=t+(2f+0.005″)

The amount of scrap generated in producing a target 20 from plate 10 canbe calculated using the following formula:Vs=(2f+0.005″)·A _(T) ·ρ _(Ta) A _(T)=target area ρ_(Ta)=0.60 lbs/in³

and the scrap credit can be calculated using the following formula:C ₅ =V _(s)(M _(s)) M_(s)=marked value of scrap V_(s)=volume of scrapC_(s)=Scrap credit

Consider the manufacturing costs of a tantalum blank 14″ in diameter(154 in²) and 0.250″ thick, and standard plate manufacturing cost(C_(5t)) of $250/lb.

Case 1 Double disc grinding of as level rolled blanks to 0.005″ flat

Assume: initial flatness f=0.075″

-   -   grinding cost=C^(g) _(m)=$50 per disc    -   grinding swarf value M_(s) ^(g)=$50/lb

Initial plate thickness g=t+(2f+0.005)

-   -   g=0.250+2(0.075)+0.005    -   g=0.405 in

Initial plate cost=g·A_(t)·ρ_(Ta)·C_(ST)(0.405 in)(154 in²)(0.60 lbs/in³)($250/lb)=$9355

Manufacturing yield t/g(0.250)/(0.405)=0.62

Scrap Credit+(2f+0.005)A_(t)·ρ_(Ta)·M_(s) ^(g)(2(0.075)+0.005)(154 in²)(0.60 lb/in³)($50/LB)=$716

Yielded manufacturing cost$\frac{\text{Initial~~Plate~~Cost}}{\text{Mfg~~Yield}} + \text{Grinding~~Cost} - \text{Scrap~~Credit}$${\frac{9355}{0.62} + 50 - 716} = {\$ 14423}$

Case 2 Press flattening and face machining to 0.005″ flat

Assume As-pressed flatness f=0.010″

-   -   Flattening Labor Cost C_(m) ^(F)=$100/disc    -   Machining Labor Cost C_(m) ^(m)=$500/disc    -   Machining Scrap Value M_(S) ^(M)=$100/lb

Initial Plate thickness=0.275″

Initial Plate cost=$6352

Manufacturing Yield=0.91

Scrap Credit=$231

Yielded Manufacturing Cost=$6999

Case 3 Machine 1 side flat to 0.005″

Assume as level rolled flatness of 0.075″

-   -   Machining Labor Cost $100/disc    -   Machining Scrap Value $100/lb

Initial plate thickness=0.405″

Initial plate cost=$9355${{Manufacturing}\quad{Yield}} = {\frac{\left( {0.405 - {f \cdot 0.005}} \right)}{(0.405)} = 80}$

Scrap Credit: (0.080)(A_(f))(ρ_(Ta))(M_(s) ^(M))=$739

Yielded Manufacturing Cost=$11055

Case 4 Press Flatten to 0.010″ and machine 1 side flat to 0.005″

Assume As-press flatness of 0.010″

-   -   Flattening Labor Cost=$100/disc    -   Machining Labor Cost=$150/disc    -   Machine Scrap Value=$100/lb    -   Initial plate thickness=0.225″

Initial plate cost=$6352${{Manufacturing}\quad{Yield}} = {\frac{0.275 - 0.010 - 0.005}{0.275} = 0.95}$

Scrap Credit(0.015)(A_(f))(ρ_(Ta))(M_(s) ^(M))=$139

Yield Manufacturing Cost=$6797

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims andequivalents thereof.

1. A method for manufacturing a metal blank, said method comprising: a)supplying at least one planar metal plate having a first surface and asecond surface, wherein said first and said second surfaces areessentially parallel; and b) flattening only said first surface of saidmetal plate whereby a metal blank is produced.
 2. The method of claim 1,wherein said metal plate comprises tantalum, copper, aluminum, titanium,niobium, cobalt, platinum, silver, gold, or alloys thereof.
 3. Themethod of claim 1, wherein said metal plate is tantalum.
 4. The methodof claim 1, wherein said metal plate is niobium.
 5. The method of claim1, wherein said first surface of said metal plate is flattened bymachining, grinding or combinations thereof.
 6. A method ofmanufacturing a metal disc, said method comprising machining said firstsurface of said metal blank produced by the method of claim 1 into adisc.
 7. The method of claim 6, wherein said metal disc comprisestantalum, copper, aluminum, titanium, niobium, cobalt, platinum, silver,gold, or alloys thereof.
 8. A method of manufacturing a metal disc, saidmethod comprising machining said first surface of said metal blankproduced by the method of claim 3 into a disc.
 9. A method ofmanufacturing a metal disc, said method comprising machining said firstsurface of said metal blank produced by the method of claim 4 into adisc.
 10. A method of forming a sputter target assembly having a metaltarget bonded to a backing plate comprising: providing a metal sputtertarget which comprises a metal disc prepared by the method of claim 6;and bonding a backing plate onto said metal disc.
 11. The method ofclaim 10, wherein said backing plate comprises copper, copper alloys,aluminum, aluminum alloys, titanium or titanium alloys or combinationsthereof.
 12. The method of claim 10, wherein said metal disc istantalum.
 13. The method of claim 10, wherein said metal disc comprisesniobium.
 14. A method of forming a sputter target assembly having ametal target bonded to a backing plate comprising the steps of:providing a metal sputter target which comprises a metal blank preparedby the method of claim 1; and bonding a backing plate onto said metalblank.
 15. The method of claim 14, wherein said metal blank comprisestantalum, copper, aluminum, titanium, niobium, cobalt, platinum, silver,gold, and alloys thereof.
 16. The method of claim 14, wherein the metalblank is tantalum.
 17. The method of claim 14, wherein the metal blankis niobium.
 18. The method of claim 1, wherein said method consistsessentially of machining one surface of said metal plate.
 19. The methodof claim 1, wherein said second surface has a flatness of about 0.075inches or less.
 20. The method of claim 1, wherein said second surfacehas a flatness of from about 0.060 inches to about 0.005 inches.
 21. Themethod of claim 1, wherein said second surface has a flatness of fromabout 0.030 inches to about 0.005 inches.
 22. The method of claim 1,wherein said first surface is machined flat to a flatness of about 0.005inches or less. 23-33. (canceled)
 34. The method of claim 14, whereinsaid metal target is bonded to said backing plate by an adhesivematerial, by soldering, by brazing, by diffusion bonding, by pressurefitting, by hot melting, or by explosion bonding.
 35. The method ofclaim 1, wherein said metal blank has a nominal thickness tolerance ofat least about 5% of the rolled gauge of the plate.
 36. The method ofclaim 1, further comprising a diameter tolerance of about +0.025/−0.00inches.
 37. A method of forming a sputter target assembly having a metaltarget bonded to a backing plate comprising the steps of: providing ametal sputter target which comprises a metal blank prepared by themethod of claim 1; and bonding a backing plate onto said metal blank,wherein said metal sputter target is tantalum and said backing platecomprises copper or an alloy thereof.
 38. The method of claim 10,further comprising providing an interlayer between said metal sputtertarget and said backing plate prior to bonding said backing plate. 39.The method of claim 1, wherein said first surface is machined flat to aflatness of about 0.010 inches or less.
 40. (canceled)